1. Field of the Invention
This invention relates to a method of making orthodontic appliances such as brackets having a textured surface for bonding the appliance to a tooth.
2. Description of the Related Art
Orthodontic treatment concerns movement of malpositioned teeth to orthodontically correct positions. During treatment, tiny orthodontic appliances known as brackets are connected to anterior, cuspid and bicuspid teeth, and an archwire is placed in a slot of the brackets. The archwire forms a track to guide movement of the teeth to desired positions for orthodontically correct occlusion. Typically, the ends of the archwire are held by appliances known as buccal tubes that are secured to molar teeth.
In previous years, orthodontic appliances such as brackets and buccal tubes were connected to teeth by welding or brazing each appliance to a band that was then placed over the desired tooth in encircling relation. In more recent years, however, it has become common practice to bond orthodontic brackets directly to the surface of the tooth. Omission of the metal bands associated with the brackets provides a more aesthetic appearance than brackets welded to bands, and helps alleviate the problem of the "metallic mouth" appearance that is often associated with orthodontic treatment.
Occasionally, brackets that are directly bonded to teeth may unintentionally debond from the surface of the teeth before treatment is completed. In some cases, bond failure is due to relatively large forces imposed on the bracket, as when the patient bites into a relatively hard food item or is unintentionally bumped in the mouth by an external object. In other instances, a bracket may debond from excessive force exerted by the archwire, such as when the orthodontist places a relatively sharp bend or twist in the archwire in an attempt to urge teeth toward desired positions. Bond failure may also be due to the use of an inadequate amount of adhesive, or due to the use of an improperly selected or improperly cured adhesive.
Premature debonding of orthodontic brackets represents a nuisance to both the orthodontist and the patient. If debonding occurs outside of the orthodontist's office, the patient must return to the office where the archwire is removed from all of the brackets and the surface of the tooth lacking the bracket is then cleaned in preparation for rebonding. Unless the debonded bracket can be cleaned of old adhesive and reused, a new bracket is selected for attachment. Next, the bracket is precisely positioned on the tooth and the adhesive is cured, following which the archwire is replaced in the bracket slots and ligated in place. As can be appreciated, such a procedure is time consuming and increases the expense and effort associated with orthodontic treatment.
The phenomena of bond failure between orthodontic brackets and the surfaces of associated teeth may arise at the location of the interface between the base of the bracket and the adhesive, in the adhesive itself, or at the interface between the adhesive and the tooth surface. Bond failures that occur between the adhesive and the base of orthodontic brackets are of particular concern to the manufacturers of brackets, and many attempts have been made over the years to improve the base of the bracket to enhance the bond of the bracket to the adhesive.
U.S. Pat. No. 4,068,379 illustrates an orthodontic bracket having a bonding base made of an initially separate mesh material that resembles a small wire screen. As the bracket is pushed into adhesive during bracket placement, the adhesive flows in and around openings of the mesh and mechanically interlocks with the mesh once the adhesive has cured. However, the mesh base is considered a significant factor in the manufacturing expense of orthodontic brackets, since such a manufacturing process often entails carefully cutting the mesh to shape, aligning the mesh with the bracket body, and then brazing the mesh to fix the mesh to the bracket body.
U.S. Pat. No. 290,040, assigned to the assignee of the present invention, illustrates an orthodontic bracket having an integral machined bonding base with substantial surface area and undercut regions for contact with the adhesive. U.S. Pat. No. 340,523, also assigned to the assignee of the present invention, illustrates an orthodontic bracket that is made of a sintered metal powder material, wherein a series of posts formed in the base during a metal injection molding operation are slightly peened over during a subsequent tumbling operation to provide a series of undercut regions.
Many orthodontists favor brackets having a base with increased surface area for bonding, and often prefer a base having a mesh pad, peened over posts or other structure that provides undercut regions, since such undercut regions provide protruding structure that hinders the adhesive from detaching from the bracket once the adhesive cures to a hardened condition. Consequently, as manufacturers search for new methods of making orthodontic appliances, increased attention has been directed toward discovering an improved method of making an orthodontic appliance that has a textured or nonsmooth bonding surface, and especially a method that provides the appliance with a bonding surface having undercut regions.